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package java.lang.management;

/**
 * The management interface for the operating system on which
 * the Java virtual machine is running.
 *
 * <p> A Java virtual machine has a single instance of the implementation
 * class of this interface.  This instance implementing this interface is
 * an <a href="ManagementFactory.html#MXBean">MXBean</a>
 * that can be obtained by calling
 * the {@link ManagementFactory#getOperatingSystemMXBean} method or
 * from the {@link ManagementFactory#getPlatformMBeanServer
 * platform <tt>MBeanServer</tt>} method.
 *
 * <p>The <tt>ObjectName</tt> for uniquely identifying the MXBean for
 * the operating system within an MBeanServer is:
 * <blockquote>
 * {@link ManagementFactory#OPERATING_SYSTEM_MXBEAN_NAME
 * <tt>java.lang:type=OperatingSystem</tt>}
 * </blockquote>
 *
 * It can be obtained by calling the
 * {@link PlatformManagedObject#getObjectName} method.
 *
 * <p> This interface defines several convenient methods for accessing
 * system properties about the operating system on which the Java
 * virtual machine is running.
 *
 * @author Mandy Chung
 * @see ManagementFactory#getPlatformMXBeans(Class)
 * @see <a href="../../../javax/management/package-summary.html"> JMX Specification.</a>
 * @see <a href="package-summary.html#examples"> Ways to Access MXBeans</a>
 * @since 1.5
 */
public interface OperatingSystemMXBean extends PlatformManagedObject {

  /**
   * Returns the operating system name.
   * This method is equivalent to <tt>System.getProperty("os.name")</tt>.
   *
   * @return the operating system name.
   * @throws java.lang.SecurityException if a security manager exists and its
   * <code>checkPropertiesAccess</code> method doesn't allow access to this system property.
   * @see java.lang.SecurityManager#checkPropertyAccess(java.lang.String)
   * @see java.lang.System#getProperty
   */
  public String getName();

  /**
   * Returns the operating system architecture.
   * This method is equivalent to <tt>System.getProperty("os.arch")</tt>.
   *
   * @return the operating system architecture.
   * @throws java.lang.SecurityException if a security manager exists and its
   * <code>checkPropertiesAccess</code> method doesn't allow access to this system property.
   * @see java.lang.SecurityManager#checkPropertyAccess(java.lang.String)
   * @see java.lang.System#getProperty
   */
  public String getArch();

  /**
   * Returns the operating system version.
   * This method is equivalent to <tt>System.getProperty("os.version")</tt>.
   *
   * @return the operating system version.
   * @throws java.lang.SecurityException if a security manager exists and its
   * <code>checkPropertiesAccess</code> method doesn't allow access to this system property.
   * @see java.lang.SecurityManager#checkPropertyAccess(java.lang.String)
   * @see java.lang.System#getProperty
   */
  public String getVersion();

  /**
   * Returns the number of processors available to the Java virtual machine.
   * This method is equivalent to the {@link Runtime#availableProcessors()}
   * method.
   * <p> This value may change during a particular invocation of
   * the virtual machine.
   *
   * @return the number of processors available to the virtual machine; never smaller than one.
   */
  public int getAvailableProcessors();

  /**
   * Returns the system load average for the last minute.
   * The system load average is the sum of the number of runnable entities
   * queued to the {@linkplain #getAvailableProcessors available processors}
   * and the number of runnable entities running on the available processors
   * averaged over a period of time.
   * The way in which the load average is calculated is operating system
   * specific but is typically a damped time-dependent average.
   * <p>
   * If the load average is not available, a negative value is returned.
   * <p>
   * This method is designed to provide a hint about the system load
   * and may be queried frequently.
   * The load average may be unavailable on some platform where it is
   * expensive to implement this method.
   *
   * @return the system load average; or a negative value if not available.
   * @since 1.6
   */
  public double getSystemLoadAverage();
}
